During the firing of clay tiles, what process occurs to create a dense, non-porous tile?

The process of vitrification is key in transforming clay tiles into dense, non-porous materials during the firing process. Vitrification occurs when clay particles are subjected to high temperatures, causing them to undergo physical and chemical changes. This process leads to the formation of a glass-like substance within the clay body, effectively filling the spaces between particles and eliminating porosity. As a result, the tiles become more durable and resistant to moisture, making them suitable for various applications, especially in construction and flooring.

In contrast, glazing involves applying a glassy coating on the surface of tiles, which enhances aesthetic appeal and provides additional surface protection but does not fundamentally alter the tile's internal structure to achieve densification. Coagulation generally refers to the process of thickening a liquid into a semi-solid state and is not relevant to the context of clay tile firing. Annealing is a heat treatment process used to reduce internal stresses and improve ductility in materials like metals, but it does not apply to the specific characteristics sought in clay tiles. Thus, vitrification stands out as the critical process that ensures the creation of a dense, non-porous tile.